To confirm you meter, using a long screwdriver or other long firm rod, insert it into the soil. It will move easily through moist soil but will not pass through dry soil easily. Once confirmed or not will determine your watering schedule.

Is it normal for clay soil to retain moisture like this?

Yes!

Ok, thanks, I guess I just have to water less as result.Maybe the scorching heat on the way will fix that? :)

Make sure you are probing the root ball. While clay soils hold lots of water, the planting mix from the container has no clay at all and may dry out quickly. It's important to keep the root ball moist (but not soggy) until roots have chance to establish in the surrounding soil.

This summer you will probably need to water at least once a week. Applying a layer of mulch on top of the soil will slow evaporation and keep the soil cooler.